We propose that folic acid and the folate methylation pathway play an essential role in repair and recovery of the injured adult CNS, and aim to investigate this relationship with the long-range goal of establishing the mechanism of action of folic acid in CNS healing. To this end, we will investigate the biochemical and molecular modifications in folate metabolism that occur in spinal cord tissue after injury, with special emphasis on the role of folate receptors and constituent folate cycle enzymes susceptible to specific antagonists. The general goals of the proposed experimental protocols are to determine the mechanism of folate entry into the cell after injury and the extent of CNS repair mediated by methylation (methionine- methylation cycle) and DNA synthesis (folate cycle), and to distinguish which specific enzymatic steps may serve as points of intervention to optimize CNS repair. These goals will be accomplished by quantifying folate-enhanced regeneration and recovery after injury in vivo in the presence and absence of specific folate and methylation cycle enzyme antagonists, together with simultaneous expression assays of the relevant enzyme-endoing genes and measurements of key folate metabolites in the injured CNS tissues (e.g., spinal cord), and differential tracing of the 2 pathways with radioactive folates. Our Specific Aims are: 1) to test the response of the folate receptor (FR-a or folate binding protein) and the dihydrofolate reductase (DHFR) genes after CNS injury. 2) To test whether methionine synthase activity is essential in providing the molecules necessary for CNS repair (methylation). And 3) to test the role of thymidylate synthase in folate- enhanced CNS repair and recovery (DNA synthesis). Successful achievement of our aims will result in a more thorough identification of the mechanism of action of folic acid in CNS recovery and repair, potentially resulting in an efficacious, low cost, low toxicity intervention that promotes recovery from CNS injury in vivo, and would be readily available for bedside trials.